Multiprotocol Label Switching (MPLS) enables efficient delivery of a wide variety of differentiated, end-to-end services. Multiprotocol Label Switching (MPLS) traffic engineering (TE) provides a mechanism for selecting efficient paths across an MPLS network based on bandwidth considerations and administrative rules. Each label switching router maintains a TE link state database with a current network topology. Once a path is computed, TE is used to maintain a forwarding state along that path.
As described in more detail in various Internet Engineering Task Force (IETF) Requests for Comment (RFC), such as RFC4726 and RFC5151, an Area Border Router (ABR) is a router located between several areas in a hierarchical Open Shortest Path First (OSPF) network. ABRs maintain topology information from multiple areas. In the case of Resource Reservation Protocol (RSVP) Inter-Domain TE-LSPs of type Contiguous LSP each Area Border Router (ABR) triggers a path computation (also referred to as an Explicit Route Object (ERO) expansion), before forwarding the RSVP Path message downstream. Thus, each ABR is responsible for calculating a TE-constrained path for its successive TE-Domain(s) or Area(s). Moreover, each ABR path computation may result in an equal cost multiple paths (ECMP) result where a tie-breaking procedure must be used to select one of the paths. For various reasons, it is preferable to ensure that the same tie-breaking procedure is used by each ABR along the LSP.